After Tuesday's hat trick, the road to victory is clear for Romney and increasingly rocky and unlikely for Rick Santorum, Romney's leading opponent.

Still, in a speech from Mars, Pa., Santorum vowed to continue his campaign.

"We have now reached the point where it's half time," Santorum said. "Who's ready to charge out of the locker room for a strong second half in Pennsylvania?"

The next contests happen April 24, when Connecticut, Delaware, New York, Rhode Island and Pennsylvania head to the polls. Pennsylvania is critical for Santorum, because it is his home state and a loss there would be seen as nothing short of devastating for his campaign.

In his victory speech, Romney gave no indication that his candidacy was being challenged. Romney ignored Santorum. Instead, he seemed to be shifting into general election mode, carefully drawing distinctions between himself and President Obama.

He painted Obama as a proponent of a "government-centered society." And he painted himself as a proponent of free enterprise.

"Washington should be an ally of business," Romney said, "not in opposition of business."

Romney made the argument that he's not trying to "transform" America, instead he wants to "restore" it to an America of small government with "strict limits."

Add to that President Obama's speech assaulting the Republican budget passed by the House and his campaign ads referring to Romney by name, and the campaign for president felt well underway.

We live blogged Tuesday night, so if you want a blow-by-blow account of how it unfolded, keep reading.

"Santorum, of course, can stay in the race as long as he likes. But, his large delegate deficit coupled with defeats in big — and symbolically important — states like Michigan, Ohio, Illinois and Wisconsin mean the political oxygen is out of the room for Santorum."

Update at 10:02 p.m. ET. Drawing Distinctions:

In his victory speech, Romney seemed to be moving on to the general election against President Obama.

He spent the bulk of his speech drawing distinctions between himself and the president. He painted Obama as proponent of a "government-centered society." And he painted himself as a proponent of free enterprise.

"Washington should be an ally of business," Romney said, "not in opposition of business."

Romney made the argument that he's not trying to "transform" America, instead he wants to "restore" it to an America of small government with "strict limits."

Update at 9:50 p.m. ET. 'We've Won Them All':

An exuberant Romney took the stage just as the AP called Wisconsin in his favor.

"We've won them all," said Romney during his speech in Milwaukee, Wis.

Update at 9:36 p.m. ET. CNN Projects Romney Wins Wisconsin:

Based on exit polls and partial results, CNN is projecting that Mitt Romney will win Wisconsin. Fox made the projection earlier in the night.

Update at 9:23 p.m. ET. 'You Know Me':

Santorum pretty much ignored today's races and focused on Pennsylvania, pleading with his supporters to stick with him.

He said that half of the country has not been heard and that he would stay in the race until the end. Then, Santorum launched into his criticism of Romney and Obama, especially on their stances on health care reform.

"If we are going to win this race, we can't have little differences between our candidate and President Obama," Santorum said. "We need to have clear, contrasting colors."

"The clock starts tonight," Santorum concluded. "The field looks a little different in May."

Update at 9:14 p.m. ET. Half Time:

In a speech in Mars, Pa., Santorum sounded subdued. Still, he vowed to continue his campaign.

"We have now reached the point where it's half time," he said. "Who's ready to charge out of the locker room for a strong second half in Pennsylvania?"

Update at 9:05 p.m. ET. CNN, NBC Project Romney Wins Washington:

CNN and NBC are calling the District of Columbia in favor of Romney. That means Romney has two wins tonight.

Update at 9 p.m. ET. Polls Close In Wisconsin:

The polls are closed now in Wisconsin. CNN provided the following exit poll numbers for the state:

-- Romney: 43 percent

-- Santorum: 35 percent

-- Ron Paul: 11 percent

-- Newt Gingrich: 6 percent

Update at 8:48 p.m. ET. Playing With Delegate Math:

The Washington Examiner's Beltway Confidential blog is doing some math taking into account Romney's Maryland win and assuming he'll win D.C. They use the AP delegate count and come to a grim conclusion for Santorum:

"In order to get to the threshold of 1,144 delegates, Romney has to win only 528 of the remaining 1,213 delegates — or 43.5%. Put the other way around: the non-Romneys have won 42.64% of all delegates to date, and in order to block Romney from winning before the convention, they would need to win 56.6% — an improvement of 32.6%."

Based on exit poll data the AP has also projected Romney will win Maryland.

CNN is reporting that according to exit polling, even voters who describe themselves as "very conservative" fell in line with Romney. The vote, which has been heavily skewed in favor of Santorum in the past, was split 40 percent to 40 percent in Maryland.

Fifty-nine percent of voters who described themselves as "somewhat conservative" voted for Romney.

CNN's exit poll found that Romney won 49 percent of the vote, while Santorum took 28 percent of the vote.

Update at 7:46 p.m. ET. Does Santorum Drop Out?

On CNN, the network's political analysts are bouncing around the question of whether Santorum will drop out of the race before the April 24 contests, which include Santorum's home state of Pennsylvania.

Ari Fleischer, who served as President George W. Bush's press secretary, said Santorum is likely just looking for a good time to quit.

"He had his chance, but he wasn't able to capitulate," Fleischer said. He predicted that if Santorum sees that polls are showing a negative outcome for him in Pennsylvania, he'll leave the race.

Donna Brazile, a Democratic political strategist, said if Santorum wins Pennsylvania he'll stay in until Texas.

April — with Connecticut, Delaware, New York and Rhode Island on the calendar — does not look good for Santorum. But May — with states like Arkansas, Kentucky and Texas headed to the polls — could play out better for Santorum.

But the panel on CNN said there's another thing weighing on Santorum's mind: The math, even if he won Pennsylvania, just doesn't add up for him.

Update at 7:35 p.m. ET. What To Expect Tonight:

From The Washington Post, here's how they're expecting the night to shape up: Santorum is expected to speak at 8 p.m. ET. from Mars, Pa.; Romney at 9 p.m. ET. from Milwaukee, Wis. and Paul at 10 p.m. ET from Chico, Calif.

Update at 7:24 p.m. ET. Santorum Supporters Losing Faith:

The New York Times is reading a bit more into the exit polls and finds that two-thirds of Santorum supporters believe Romney will be the eventual nominee. Only 30 percent of his supporters believe Santorum will win.

"And most voters on Tuesday are just fine with Mr. Romney at the top of the party's ticket.

"About two-thirds say they would be satisfied if Mr. Romney won the nomination. But here Mr. Santorum's supporters are less enthused. About 4 in 10 of them say they would be satisfied with Mr. Romney, while nearly 6 in 10 would be dissatisfied."

In Wisconsin, the recall election of Gov. Scott Walker has in some ways overshadowed the GOP nomination campaign. The Washington Post's Chris Cillizza reports that according to exit polls 80 percent of voters in Wisconsin approve of him.

Those numbers, writes Cillizza, reflect "the remarkable polarization in the electorate as he prepares for a June 5 recall election."

Cillizza adds:

"In an NBC/Marist poll conducted in Wisconsin last week, 48 percent of people approved of the job Walker is doing while an equal 48 percent disapproved. Among Republicans, 91 percent approved of how Walker was handling his job while 84 percent of Democrats disapproved. Independents split right down the middle — 47 percent approval/47 percent disapproval.

"What that slew of data means is simple. If you like Scott Walker, you LOVE him. If you don't like Scott Walker, you HATE him. And virtually everyone in the state is in one of those two camps."

Update at 7:02 p.m. ET. 80 Percent Say Romney Will Be GOP Candidate:

In Wisconsin the exit polls are showing that many of the voters tonight think this race is over.

ABC News reports that 80 percent of voters expect Romney to be the party's eventual nominee.

ABC adds that this electorate was also less concerned about a candidate who shares their religious belief and were more concerned with electability.

"A majority picks either electability in November or 'the right experience' as the candidate attribute of chief concern, both winning qualities for Romney to date," ABC reports.